diff options
| author | François Freitag <mail@franek.fr> | 2016-06-03 15:31:21 -0700 |
|---|---|---|
| committer | Tim Graham <timograham@gmail.com> | 2017-01-11 09:25:37 -0500 |
| commit | f3b7c059367a4e82bbfc7e4f0d42b10975e79f0c (patch) | |
| tree | d64dedfcd04cfbe8d7599aa6411597cccba6eb17 /docs/ref | |
| parent | 53bffe8d03f01bd3214a5404998cb965fb28cd0b (diff) | |
Refs #16614 -- Made QuerySet.iterator() use server-side cursors on PostgreSQL.
Thanks to Josh Smeaton for the idea of implementing server-side cursors
in PostgreSQL from the iterator method, and Anssi Kääriäinen and Kevin
Turner for their previous work. Also Simon Charette and Tim Graham for
review.
Diffstat (limited to 'docs/ref')
| -rw-r--r-- | docs/ref/databases.txt | 18 | ||||
| -rw-r--r-- | docs/ref/models/querysets.txt | 14 |
2 files changed, 25 insertions, 7 deletions
diff --git a/docs/ref/databases.txt b/docs/ref/databases.txt index 51feceea04..16addc52bc 100644 --- a/docs/ref/databases.txt +++ b/docs/ref/databases.txt @@ -171,6 +171,24 @@ If you need to add a PostgreSQL extension (like ``hstore``, ``postgis``, etc.) using a migration, use the :class:`~django.contrib.postgres.operations.CreateExtension` operation. +.. _postgresql-server-side-cursors: + +Server-side cursors +------------------- + +.. versionadded:: 1.11 + +When using :meth:`QuerySet.iterator() +<django.db.models.query.QuerySet.iterator>`, Django opens a :ref:`server-side +cursor <psycopg2:server-side-cursors>`. By default, PostgreSQL assumes that +only the first 10% of the results of cursor queries will be fetched. The query +planner spends less time planning the query and starts returning results +faster, but this could diminish performance if more than 10% of the results are +retrieved. PostgreSQL's assumptions on the number of rows retrieved for a +cursor query is controlled with the `cursor_tuple_fraction`_ option. + +.. _cursor_tuple_fraction: https://www.postgresql.org/docs/current/static/runtime-config-query.html#GUC-CURSOR-TUPLE-FRACTION + Test database templates ----------------------- diff --git a/docs/ref/models/querysets.txt b/docs/ref/models/querysets.txt index 3090251659..5fe783514d 100644 --- a/docs/ref/models/querysets.txt +++ b/docs/ref/models/querysets.txt @@ -1981,15 +1981,15 @@ evaluated will force it to evaluate again, repeating the query. Also, use of ``iterator()`` causes previous ``prefetch_related()`` calls to be ignored since these two optimizations do not make sense together. -.. warning:: +Some Python database drivers still load the entire result set into memory, but +won't cache results after iterating over them. Oracle and :ref:`PostgreSQL +<postgresql-server-side-cursors>` use server-side cursors to stream results +from the database without loading the entire result set into memory. + +.. versionchanged:: 1.11 - Some Python database drivers like ``psycopg2`` perform caching if using - client side cursors (instantiated with ``connection.cursor()`` and what - Django's ORM uses). Using ``iterator()`` does not affect caching at the - database driver level. To disable this caching, look at `server side - cursors`_. + PostgreSQL support for server-side cursors was added. -.. _server side cursors: http://initd.org/psycopg/docs/usage.html#server-side-cursors ``latest()`` ~~~~~~~~~~~~ |